#9163: Ptr should have a phantom role -------------------------------------+------------------------------------ Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by simonpj): Richard says: It seemed clear to me that `Ptr` ''should'' be representational, thinking that we don't want to coerce a `Ptr Int` to a `Ptr Bool`. I don't see any reason why this couldn't be changed. Why is `Ptr` a `data` not a `newtype`? If it were a newtype, we could keep the role annotation and use `coerce` internally, according to the updated Coercible solver. Answer (from Simon): because the payload is an unboxed `Addr#`, so `Ptr` boxes it. A `newtype` can't have an unboxed payload. However, it is crucial that `FunPtr` have a representational argument, as normaliseFfiType' depends on this fact. There is a brief comment in `TcForeign`, but clearly more comments are necessary. Will do shortly. If we want to change `FunPtr`'s role, `normaliseFfiType'` would have to be updated, too, but it shouldn't be hard. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9163#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler